Sorry, when I said it was hard to get A4 in the US, I was referring to the heavier grade card stock that that is usually used for paper models. A4 copy paper is definitely available, but I would strongly advise against making paper models out of it, especially anything of any size. I have yet to find a dependable source for 100-110lb. card stock in A4 in the US and I would be thrilled if anyone knows of a supplier!
Chris